Metering valves are a common means by which aerosols are dispensed from aerosol containers. Metering valves are particularly useful for administering medicinal formulations that may include a liquefied gas propellant and are delivered to a patient in an aerosol.
When administering medicinal formulations, a dose of formulation sufficient to produce the desired physiological response is delivered to the patient. The proper, predetermined amount of the formulation must be dispensed to the patient in each successive dose. Thus, any dispensing system must be able to dispense doses of the medicinal formulation accurately and reliably to help assure the safety and efficacy of the treatment.
Metering valves have been developed to provide control over the dispensing of medicinal aerosol formulations. A metering valve regulates the volume of a medicinal formulation passing from a container to a metering chamber. A metering chamber typically is formed in a space between a structural portion of the metering valve such as a valve body and a moveable portion of the metering valve such as a valve stem. The metering chamber also may be defined, in part, by one or more fluid tight seals, each of which may be formed between, for example, an annular gasket and the valve stem. One such annular gasket may be a metering gasket that serves to isolate the metering chamber from a container holding the bulk formulation. Each seal generally is designed to remain fluid tight even when the valve stem slides past the gasket when the valve stem is actuated. A gasket and the valve stem generally are configured so that each conforms to the shape of the other, thereby facilitating the desired fluid tight seal. Depending upon the particular design of the metering valve, the metering chamber may be formed prior to or during actuation of the valve stem.
However, the valve stem may include additional surface features that may cause deterioration of the fluid tight seal between a gasket and the valve stem upon repeated actuation of the valve stem. For example, the valve stem may include an internal channel through which formulation flows in order to fill the metering chamber. The channel opening may have one or more sharp edges that can damage a metering gasket upon repeated actuation of the valve stem.
Damage to a gasket such as a metering gasket can degrade the seal between the gasket and the valve stem, thereby corrupting dose metering, contaminating the formulation with particles of gasket material, or both. Damage to a gasket also may block or partially block delivery of the formulation. This may occur directly, such as by accumulation of gasket fragments. Alternatively, the effect may be indirect; abraded gasket particles may act as “seeding” for precipitation or deposition of the formulation. Delivery of formulation may be completely or partially blocked by accumulated gasket particles, precipitated or deposited formulation, or both. Also, damage to a gasket may result in increased, unpredictable or uneven friction forces between the valve stem and the gasket. Such damage may require more force to actuate the metering valve to obtain a dose of formulation or otherwise adversely affect operation of the metering valve, resulting in inconsistent or improper dosing of formulation.
A related problem observed in some metering valves is that of seal intrusion, i.e., a gasket such as a metering gasket may intrude into an opening that exists in a portion of the metering valve. Even if the gasket sustains no substantial damage as a result of seal intrusion, performance of the metering valve may be compromised. For example, after a gasket intrudes into an opening, it subsequently must be removed from the opening in order to allow continued function of the metering valve, either continued actuation or a return to its resting position. Deforming the gasket sufficiently to remove the gasket from the opening may require substantial additional force. Such deforming of the gasket may be sufficient to render the gasket unable to reset the fluid tight seal with the valve stem, thereby compromising performance of the valve stem.
A gasket that intrudes into an opening may become lodged therein if it cannot be completely removed from the opening. This may lead to jamming of the metering valve and, therefore, partial or complete loss of performance. Seal intrusion also may require that an inconsistent, or even a consistent but higher, amount of force be applied in order to actuate the metering valve. Thus, metering valves susceptible to seal intrusion may be more difficult for a patient to use properly and, therefore, the patient may fail to obtain the prescribed dose of formulation.
Therefore, a need exists for a valve stem for use in an aerosol metering valve that is designed to limit the likelihood and extent of seal intrusion. A further need exists for a valve stem for use in an aerosol metering valve that is designed to limit damage to the metering gasket caused by seal intrusion, particularly upon repeated actuation of the metering valve.